The present invention is directed to a circuit arrangement for a subscriber-remote termination of a subscriber line, high bit rate data signals and analog telephone signals being transmitted over a two-lead copper line.
The subscriber-remote termination of a subscriber line is in the form of a two-lead copper line. In addition to telephone signals in the voice band that are exchanged between the telephone set of a subscriber terminal equipment and a telephone exchange, a high-rate data signal stream in the direction from a subscriber-remote central to the subscriber terminal equipment and a data signal stream in the direction from the subscriber terminal equipment to the central having a lower rate compared thereto are transmitted in a frequency band that is above the voice band.
Such a utilization of existing subscriber lines in the form of a two-lead copper line is possible because of what is referred to as ADSL technology (Asynchronous Digital Subscriber Line) that identifies one of the transmission systems for new possibilities of utilizing existing, high-quality copper line networks. This is an alternative to the installation of new line networks for new communication services because of the high capital costs of copper line networks.
ADSL technology was originally provided for the transmission of demand services and, in particular, in conjunction with the individual retrieval of television programs (see, for example, ntz, No. 4/1995, pp. 28 ff.).
In this context, a high-rate digital signal from a central to the terminal equipment as well as a potentially bidirectional, lower-rate control signal between central and terminal equipment are transmitted over a main telephone terminal in addition to telephone signals that are exchanged between a telephone set of a terminal equipment and a telephone exchange. Via the control channel, the subscriber can designationally select, for example, video information in a server and have this played to the home tv set of the terminal equipment via the high-rate channel. According to the European standard, transmission rates of 2.048 Mbit/s, 4.096 Mbit/s as well as 6.144 Mbit/s are provided for the high-rate channel, 16 Kbit/s, 64 Kbit/s or 640 Kbit/s for the control channel.
Currently, ADSL technology is accorded greater significance for the access of terminal equipment to the Internet via telephone exchanges. In order to prevent a mutual influencing of analog telephone signals and the data signals of the ADSL method, the latter occupy a frequency range lying above the voice band.
Devices for separating and for merging telephone signals and data signals, (what are referred to as POTS splitters), as well as modems with which the complicated modulation and demodulation procedures applied in this context are executed (quadrature amplitude modulation QAM) are required both at the subscriber side as well as at the exchange side in conjunction with the ADSL method.
In previous line networks in ADSL technology, the equipment of the exchange side, i.e. splitters and modems, required in conjunction with the handling of the data signals were autonomous devices that had to be designed for protection against overvoltage since overvoltages transmitted there onto from the subscriber line can reach them (see, for example, the product information of the company analog devices "ADSL Solutions-AD20 msp 910"). Considerable additional space requirement is required in the exchange area, resulting in the required overvoltage protection circuit substantially contributing to the equipment costs.